I am living in an apartment on the last floor of a small apartment building. The ceiling is a "cathedral ceiling", in that it slopes down from the left of a mezzanine down to the level of the window. In the middle there is an arched window which the ceiling is designed with giving an v shape down the middle.

After the winter I noticed evidence of water infiltration (I live in Canada), though I am not sure how to go about trying to find the cause. While I am happy to do DIY I am feeling this is something that will need a professional. The only catch is which one? Should I be getting a general building inspector to come in and look at the issue, in order to get the right type of contractor in, or should I being making use of a roofing contractor?